In wireless communications systems, such as an Analog Mobile Phone System (AMPS) or a Global Standard for Mobile Communications (GSM) system, call processing includes call origination and termination. For example, a call originated by a wireless calling party to a wireline called party must be connected through a mobile communications network, such as a Public Land Mobile Network (PLMN), to a land-based communications network, such as a Public Switched Telephone Network (PSTN). The setup of the call, however, often involves different types of calls (e.g., different trunking protocols such as GSM, ISUP, TIJP and R2) required to establish a call connection, each trunking protocol requiring a call state machine capable of originating and terminating calls for the particular call types. Each call state machine can generate and communicate its own types of messages (e.g., call setup signaling) but the call setup messages for different call types are incompatible with the call setup messages of other call types. Call setup messages include information such as calling party number, called party number, call type (e.g., data or voice) and other information needed by the particular call type.
In conventional communication systems, there may be a single agent, for example a software entity, capable of handling the call messaging for all call types or an agent for each call type involved in establishing a call connection. A problem arises, however, in the interworking of the different external interfaces for different call types as the call signaling for each call type involved in establishing a single call connection may be unique and incompatible with other call type signaling. Thus, in conventional communication systems, each agent (whether a single agent for all call types or a separate agent for each call type) requires knowledge of each call type handled by the communications system, thereby adding complexity to each agent as well as presenting integration and maintainability problems as more call types are added to the communications system.